In vehicle drive units, particularly for working machines, that comprise a hydrostatically driven transmission, or in the case of a hydrostatically power-branched continuously variable powershift transmission, or in drive-trains with powershift transmissions having a hydrodynamic torque converter, or of electric drives, there is a so-termed inching function. For inching, by way of an additional brake pedal, the traction force of the drive unit is changed from 100% to 0%. In working machines the inching function is used in driving situations when a high engine rotational speed is needed for the hydraulic pump connected to an auxiliary power takeoff, but the travel speed has to be regulated to zero while the engine speed must remain high. Such driving situations, particularly in the case of wheel loaders, can be for example: inching on level ground when driving onto a truck while at the same time raising the scoop, inching on aggregate so that the full hydraulic power is available for filling and lifting the scoop, and inching while driving on a ramp where the scoop, for subsequent tipping, has to be raised already while driving.
The power that the inching clutch has to take up during inching depends on the one hand on the torque required and the drive engine rotational speed and the travel speed called for by the driver. In this slipping condition of the inching clutch the power at the inching clutch is a function of the rotational speed difference produced and the torque required. If the rotational speed difference or the torque required, and hence the power at the inching clutch are too high, the inching clutch can become overheated. The maximum possible rotational speed difference of the inching clutch occurs when the vehicle is stationary and the driver fully depresses the gas pedal. Thus, the level of the engine rotational speed depends on the engine characteristics. The level of the torque produced is as a rule limited by an applied maximum permissible torque. Thus, in any application, depending on the engine rotational speed a different maximum power is produced at the inching clutch. This can result in overstepping the maximum permissible power of the inching clutch.
DE 10 2007 017 175 A1 and DE 10 2012 212 653 A1 disclose methods for transmitting the power of an inching clutch.